Cardiac pacemaker with hystersis behavior

Abstract

A pacemaker having a hysteresis feature which permits intrinsic heart activity, controlled by the sinus node to resume optimally after pacing. The pacemaker has a programmable lower rate and upper rate, a programmable lower hysteresis rate (LRH) corresponding to a lower rate hysteresis interval (LRHI), and a programmable rate (IR) intermediate an upper pacing rate (UR) and a lower pacing rate (LR). A microprocessor measures the average rate of change M AVG in the intervals between consecutive ventricular depolarizations, and compares the last intrinsic escape interval RR N to the lower rate hysteresis interval (LRHI). If the last intrinsic escape interval RR N is longer than the lower rate hysteresis interval (LRHI), and if the value of M AVG is greater than a first preselected value SL 1 but less than a second preselected value SL 2 , the pacemaker stimulates at the lower rate hysteresis (LRH) and thereafter gradually increases the pacing rate up to the intermediate rate (IR). A time counter maintains a continuous pacing at the intermediate rate (IR) for a predefined period of time, and the pacing rate is gradually decreased toward the lower pacing rate (LR).

What is claimed is:  
     
       1. In a pacemaker having a programmable lower rate and upper rate, a programmable lower rate hysteresis (LRH) corresponding to a lower rate hysteresis interval (LRHI), and a programmable intermediate pacing rate (IR) the improvement comprising: 
       A. means for measuring rate of change M AVG  of successive cardiac intrinsic escape intervals;  
       B. means for comparing M AVG  to a first predefined limit SL 1 ;  
       C. means for comparing the last intrinsic escape interval to the lower rate hysteresis interval (LRHI); and  
       D. means for stimulating a heart at the lower rate hysteresis (LRH) and for gradually incrementing a pacing rate until the pacing ratio reaches the intermediate pacing rate (IR) if the last intrinsic escape interval is longer than the lower rate hysteresis interval (LRHI) and if said M AVG  is greater than SL 1 .  
     
     
       2. The pacemaker according to claim  1  further comprising: 
       A. time counter means for maintaining continuous pacing at the intermediate rate (IR) for a predefined period of time; and  
       B. means for allowing gradual decay of the pacing rate after said selected period of time has lapsed.  
     
     
       3. The pacemaker according to claim  2 , wherein said selected programmable time is set equal to five minutes. 
     
     
       4. The pacemaker according to claim  1 , wherein said means for measuring the rate of change M AVG  comprising: 
       A. means for measuring intervals between two successive ventricular depolarizations (RR intervals); and  
       B. means for averaging the rate of change M AVG  of said successive RR intervals.  
     
     
       5. The pacemaker according to claim  4 , wherein said means for averaging the rate of change of said RR intervals comprises: 
       A. means for calculating a difference D between two successive RR intervals;  
       B. means for comparing said difference D to a predetermined reference value;  
       C. means for storing those values of D which are greater than said reference value;  
       D. means for calculating a sum M of N stored values of D, wherein N is a predetermined positive integer; and  
       E. means for setting M AVG  equal to M/N.  
     
     
       6. The pacemaker according to claim  5 , wherein said means for averaging M AVG  comprising means for averaging the values of D greater than said reference value over a predefined period of time. 
     
     
       7. The pacemaker according to claim  6 , wherein said reference value is zero, and wherein only positive values of D are stored and added. 
     
     
       8. The pacemaker according to claim  5 , wherein N is set equal to six beats. 
     
     
       9. The pacemaker according to claim  4 , further including means for comparing M AVG  to a second predetermined limit SL 2  wherein SL 2  has a value greater than that of SL 1 . 
     
     
       10. The pacemaker according to claim  9 , wherein said means for stimulating gradually increments the pacing rate until the pacing rate reaches the intermediate pacing rate (IR), if the last intrinsic escape interval RR N  is longer than LRHI, and if M AVG  is greater than or equal to SL 1  but less than or equal to SL 2 . 
     
     
       11. The pacemaker according to claim  9 , further comprising means for inhibiting stimulation if M AVG  is greater than SL 2 , and if the RR N  interval is less than or equal to LRHI. 
     
     
       12. The pacemaker according to claim  11 , further comprising means for stimulating at the lower rate if M AVG  is greater than SL 2 , and if the RRN interval will be longer than LRHI. 
     
     
       13. The pacemaker according to claim  11 , further comprising: 
       A. means for inhibiting stimulation if M AVG  is greater than SL 2 , and if the RR N  interval is less than or equal to LRH; and  
       B. means for stimulating at the lower rate if M AVG  is greater than SL 2 , and if the RR N  interval will be longer than LRHI.  
     
     
       14. The pacemaker according to claim  4 , further including means for inhibiting stimulation if M AVG  is less than SL 1 , and if the last intrinsic escape interval RR N  is less than or equal to LRHI. 
     
     
       15. The pacemaker according to claim  14 , further comprising means for stimulating at the lower rate if M AVG  is less than SL 1 , and if the RR N  interval will be greater than LRHI. 
     
     
       16. A method for pacing with a pacemaker having a programmable lower rate and upper rate, a programmable lower hysteresis rate (LRH) corresponding to a lower rate hysteresis interval (LRHI), and a programmable intermediate pacing rate (IR), the pacing method comprising the steps of: 
       A. measuring a rate of change of M AVG  of successive intrinsic escape intervals;  
       B. comparing M AVG  to a first predetermined limit SL 1 ;  
       C. comparing a last intrinsic escape interval RR N  to the lower rate hysteresis interval (LRHI); and  
       D. stimulating at the lower rate hysteresis (LRH) and gradually incrementing a pacing rate until it reaches the intermediate pacing rate (IR) if the RR N  interval will be longer than the lower rate hysteresis interval (LRHI) and if said M AVG  is greater than SL 1 .  
     
     
       17. The pacing method according to claim  16  further comprising the steps of: 
       A. maintaining continuous pacing at the intermediate rate (IR) for a predefined period of time; and  
       B. allowing gradual decay of the pacing rate after said selected period of time has lapsed.  
     
     
       18. The pacing method according to claim  17 , wherein, said step of measuring the rate of change M AVG  comprises: 
       A. measuring intervals between two successive ventricular depolarizations (RR intervals); and  
       B. averaging the rate of change M AVG  of said successive RR intervals;  
     
     
       19. The pacing method according to claim  18 , wherein said step of averaging the rate of change of said RR intervals comprises: 
       A. calculating a difference D between two successive RR intervals;  
       B. comparing the difference D to a predetermined reference value;  
       C. storing those values of D which are greater than said reference value;  
       D. calculating a sum M of N stored values of D, wherein N is a predetermined positive integer; and  
       E. setting M AVG  equal to M/N.  
     
     
       20. The pacing method according to claim  19 , further comprising the step comparing M AVG  to a second predetermined limit SL 2 , wherein SL 2  has a value greater than that of SL 1 . 
     
     
       21. The pacing method according to claim  20 , wherein said step of stimulating comprises gradually incrementing the pacing rate until it reaches the intermediate pacing rate (IR), if the RRN interval will be longer than LRHI, and if M AVG  is greater than or equal to SL 1  but less than or equal to SL 2 . 
     
     
       22. The pacing method according to claim  18 , further comprises: 
       A. the step of inhibiting stimulation if M AVG  is less than SL 1 , and if the last sensed RR interval is less than or equal to LRHI;  
       B. the step of stimulating at the lower rate if M AVG  is less than SL 1 , and if the RR N  interval will be longer than LRHI;  
       C. the step of inhibiting stimulation if M AVG  is greater than SL 2 , and if the RR N  interval is less than or equal to LRHI; and  
       D. the step of stimulating at the lower rate if M AVG  is greater than SL 2 , and if the RR N  interval will be longer than LRHI.  
     
     
       23. A cardiac pacemaker comprising: 
       
         means for sensing depolarizations,  
       
       
         means for controlling the timing and delivery of pacing pulses to a heart, means for measuring the rate of depolarization from said sensed depolarizations and means for comparing the current rate to a recent past average rate and from said determining the rate of decrease, and means responsive to said means for determining rate decrease for generating control signals to said control means for pacing at predetermined rates above a lower pacing rate if said rate of decrease exceeds predetermined amounts.  
       
     
     
       24. A method of pacing the heat including the steps: 
           1   )  sensing electrical depolarizations within a heart chamber,    
           2   )  making a determination based on sensed depolarizations in said chamber of the intrinsic heart rate,    
           3   )  comparing the current intrinsic heart rate with previously sensed intrinsic heart rate to determine whether a rapid drop in heart rate of a predetermined size has occurred,    
           4   )  on the discovery of a rapid drop in heart rate of said predetermined size, pacing at predetermined rates higher than a lower pacing rate.    
     
     
       25. A method according to claim  22  further comprising after step  4 : 
       
         decreasing the pacing rate gradually until either an intrinsic rate is established above the lower rate or the lower rate is reached whereupon pacing continues at the lower rate.  
       
     
     
       26. The method as set forth in claim  24  wherein if the activity sensor indicates a sensor rate that is higher than the lower rate, pacing at the sensor rate.  
     
     
       27. A cardiac pacemaker, as set forth in claim  23  and further comprising means for decreasing the pacing rate gradually until either an intrinsic rate is established above the lower rate or the lower rate is reached whereupon pacing continues at the lower rate.  
     
     
       28. A cardiac pacemaker as set forth in claim  27  further comprising means for pacing at an activity sensor rate if said activity sensor rate is higher than the lower.  
     
     
       29. A heart stimulator comprising: 
       
         pulse generator means for generating and emitting stimulation pulses to a heart at a rate;  
       
       
         detector means for sensing events in said heart, including spontaneous heartbeats; and  
       
       
         control means, connected to said pulse generator means and to said detector means, for controlling the emission of stimulation pulses by said pulse generator means for causing the emission of a stimulation pulse if a spontaneous heartbeat rate as sensed by said detector means drops below a defined lower rate within a predetermined period and for causing said pulse generator means, when said spontaneous heartbeat rate falls below said defined lower rate within said period, to emit said stimulation pulses at rates faster than said defined lower rate.  
       
     
     
       30. A heart stimulator as set forth in claim  29  wherein after emitting said stimulation pulses at a rate faster than said lower rate, said control means subsequently slows the rate of emission of said stimulation pulses down to said defined lower rate.  
     
     
       31. A heart stimulator as in claim  29  or  30  wherein if a sensor rate is higher than said defined lower rate, said, said means for controlling the timing and delivery of pacing pulses paces at a rate indicated by said sensor rate.